Production of acetylene



Patented July 10, 1934 PATENT OFFICE PRODUCTION OF ACETYLENE James Burgin, Oakland, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application October 6, 1931,

Serial No. 567,300

17 Claims. (01. 260-170) This invention relates to the production of acetylene from hydrocarbons such as the paraflin hydrocarbons, olefine hydrocarbons, aromatic hydrocarbons, naphthefies, natural gas which contains a preponderance of methane, casinghead gas vapors, industrial gases containing hydrocarbons and the like. More particularly, the invention is concerned with the incomplete combustion of said raw material with oxygen, air or an oxygen-containing gas, the process being executed at or above the ignition temperature of the gaseous mixture.

.In cracking methane or other hydrocarbons to acetylene without the use of oxygen or an oxygencontaining gas, great difiiculties are experienced in executing the process due to the fact that the apparatus employed is of short life under the drastic conditions of pyrogenesis and that coking is more or less unavoidable, entailing great expense in the operation of said method.

I have found that when hydrocarbons, natural gas or the like are subjected to incomplete combustion with pure oxygen or gases containing oxygen while confining the heat of combustion in the reaction zone, relatively high yields of acetylene are made possible with minimum inconvenience and expense. The heat of combustion can be confined in the reaction zone in a variety of ways depending upon the particular method selected for incomplete combustion.

For example, an explosive mixture of hydrocarbon and oxygen may be burned in an apparatus as follows: The gaseous mixture exits from the burner nozzle at a linear gas velocity above the respective flame velocity of the gas mixture. Due to its gas velocity, the flame tends to tear itself away from the mouth of the burner and become extinguished. By maintaining auxiliary nozzles adjacent to the main burner nozzle, to 40 which auxiliary nozzles is fed pure oxy n, a gaseous mixture containing the same components as the main mixture but possessing a greater oxygen content, or to which is fed a gaseous mixture of the same composition as that in the main burner-nozzle, the pilot flames burning from the auxiliary nozzles maintain flame combustion by confining the heat of combustion in the immediate reaction zone. The gas mixture emerges from the auxiliary nozzles at a velocity below the respective flame velocity of the gas. When pure oxygen is employed, it burns as an inverted flame in the rest of the gas mixture. In operating in the manner described, one is enabled to use a critically lean mixture of hydrocarbon and oxy- 5 gen, thereby involving a saving in the amount of oxygen necessary for combustion. For mixtures containing methane and oxygen, the ratio can exceed 1:1, the optimum in a small apparatus being substantially 1.321 but increasing with the size of the apparatus.

The oxygen fed to the pilot jets can be combined with other combustible gases such as hydrogen and the like. Since the operation yields hydrogen as well as acetylene, it is desirable, from an economic viewpoint, to recycle the same. The ,5 presence of hydrogen in the reaction mixture favors the yield of acetylene in that it enables the maximum yield to be obtained at a higher space velocity. These pilot flames aid the combustion of the gaseous mixture in a closed tube with a relatively small proportion of oxygen which isnot possible with another kind of oxygen-gas burnerthus also avoiding the risk of producing an explosive mixture. Gas flames with a low oxygen: hydrocarbon ratio favor the formation of 15 acetylene. By this arrangement, the heat of combustion is confined in the reaction zone as the main flame burns in an outside atmosphere created by the discharged gases of the flame. The gaseous mixture can be burned in any direc- 30 tion, horizontal, vertical, upwards or downwards, in various surrounding. media such as hydrocarbons, natural gas, carbon monoxide, carbon dioxide, nitrogen, hydrogen, steam or the like. When the flame is burned in a metal tube which sur- 86 rounds the flame, said tube is preferably cooled by conventional means to prevent the decomposition of acetylene, due to the catalytic effect of a hot metallic surface.

When it is desired to dispense with pilot flames, .0 use may be made of a tube into which the gaseous mixture is fed. Heat is externally applied to the tube to raise the gaseous mixture to its ignition temperature. Once the reaction is initiated, heat is developed due to the exothermic 05 character of reaction. In the absence of a large proportion of nitrogen, the reaction is substantially autothermic. Accordingly only such quantity of heat is supplied to the surface of the tube as will substantially confine the heat of combustion in the reaction zone, as otherwise the flame would die out due to the linear gas velocity being above the respective flame velocity of the gas mixture. The tube may or may not be composed of porous or refractory ceramic materials, ,'such as quartz, silica, porcelain or alundum, caradvantageous results. The heat supplied to the tube should be suiflcient to keep the gaseous mix ture ignited in the tube. I have found that de-; sirable yields of acetylene are realized by the incomplete combustion of the gaseous mixture at temperatures above 850 0., preferably at about 1000 C. or higher. It is preferable that the inside diameter of the tube be relatively small.

The time of exposure of the gases to the high temperature aflects the yield of acetylene. When the temperature of the tube is raised, the space velocity may be correspondingly increased in order to obtain the maximum yield of acetylene.

Hydrogen as well as otherinflammable gases may be added to thehydrocarbon-oxygen mixture for burning in the main flame in order 'to increase the speed of the flame propagation. The hydrogen may be obtained from any source and may even be utilized as a by-product of the pyrolytic conversion.

If desired, the gaseous mixture may be burned in a tube containing material of a refractory nature such as quartz, silica, porcelain, pumice, alundum or the like, to facilitate heat transfer to the gas. The refractory material may be utilized in any form as granular packing, bundles of parallel tubes, or may exist as one piece having channels, slots or annular spaces. It is preferable to employ such refractory tubes with relatively small inside diameters. The material is heated to a temperature suitable to initiate the ignitionof the gaseous'mixture. Due to the exothermic character of the oxidation reaction, suflicient heat is involved to maintain the burning of the gaseous mixture despite the fact that the gas is introduced into the tube at a linear velocity greater than the respective flame velocity of thegas mixture. Where a gaseous mixture of hydrocarbon and oxygen is flowed at a gas velocity greater than the velocity of the free flame, the interpositicning of a refractory material in the path of said gas flow will cause the maintenance of said flame due to the surface action of the refractory material in speeding up the velocity of combustion.

As the reaction proceeds without the further external application of heat, the reaction zones tend to wander awayfrom the burner-nozzle when the velocity of combustion of the gaseous mixture on the surface of the refractory material is less than the gas velocity. Where the explosive mixture is employed, no harm is caused by such phenomenon, as the gaseous mixture is introduced at the other end of the tube when the reaction zone is adjacent thereto. In other words, the direction of operation is intermittently reversible. However, the reaction zone can be fixed by the external application of heat sufficient to maintain the heat of combustion in the reaction zone or by progressively increasing the oxygen content in the gaseous mixture, however maintaining at all times a gas velocity greater than the flame velocity of the gas mixture.

When the process is carried out in a tube packed with refractory materials, using air, air mixed with oxygen or other reaction mixtures containing inert gases instead of substantially pure oxygen, the heat of reaction for a given gas volume is restricted and is insuflicient for selfsupport. Use then can be made of the intermittent heating of the reaction zone by the combustion of any type of fuel. For example, the efiluent gas from which the acetylene has been scrubbed may be burned in the reaction chamber packed with refractory material, whereby the heat of combustion is accumulated in said material. ture is passed in the same direction through the reaction chamber and the confined heat of com bustion is utilized to support the reaction. The reaction zone will wander in the manner described previously. When it has reached the end of the reaction chamber, the flow of the reaction mixture is stopped and the refractory material is again internally heated by the combustion of a fuel with air, the direction of the flow ofheating gas being now opposite to that of heretofore.

. After the desired temperature is reached, the

heating is discontinued and the reaction mixture is again passed through the hot refractory material, this time in the direction opposite to that employed in the first period. The direction of operation is thus intermittently reversible with lean oxygen mixtures as with substantially rich oxygen mixtures, the. only difference being that in the former the fiow ofthe explosive reaction mixture is intermittently discontinued while heatingof the refractory material is being brought about. Instead of the internal application of heat, use may be made of the intermittent external application of heat.

Still another modification may be availed of in the general application of the process. The reaction zone may be heated by conducting the effiuent gases back through channels adjacent to the reaction zone thus confining the heat to the reaction zone by contercurrent heat exchange. The reaction zone may or may not be packed with refractory material, although it is preferable in the former state.

My invention is not restricted to the use of normally gaseous hydrocarbons nor to mixtures of the same as it can be utilized with liquid hydrocarbons which have been first vaporized by any suitable means. Further, gases resulting from the destructive distillation of coal and the like can be used to advantage in my process, the presence of inflammable gases increasing the speed of the flame propagation, whereas the presence of inert gas such as described heretofore enhances the economy of the process.

If desired, control on the speed of propagation of the flame may be affected through the use of an electrical field maintained in the reaction zone.

By way of illustration only reference will be had to certain examples of my procedure.

(1) Through a quartz tube of 4.3 mm. and a heating length of 30 cm., a gas mixture of 56% CH4 and 44% 02 was passed with a velocity of 740 cc. per minute at ignition-temperature. A concentration of 6.4% C2H2 was found in the eflluent gas.

(2) Through a silica tube 4.75 mm. diameter and a heating length of 68 cm., a natural gasoxygen mixture in the ratio 1.4:1 was passed at a flow of 8.6 liters per minute. The furnace temperature was kept around 1100 C. The efiluent gas container 10.0% C2H2.

(3) A natural gas-oxygen mixture of the ratio 1.43:1 and a total gas velocity of 4540 cc. per minute was burned under atmospheric pressure with the above described burner tip. The surrounding pyrex tube had a diameter of 1.7 cm., was vertical, and the flame was directed downwards. The collected combustion gas contained a concentration of 6.9% C2H2.

(4) A burner tube nozzle of inside diameter surrounded by auxiliary nozzles was fed with a mixture of 200 cu. ft. per hour of methane and 144 cu, ft. per hour of oxygen which was ignited.

Subsequently, the explosive reaction mix- A concentration of 5.6% acetylene was obtained in the outgoing gas.

(5) Through "a bundle of 17 alundum tubes (internal diameter 1.5 mm. and length 15 cm.) in a quartz tube, a mixture of methane and oxygen in the ratio of 1.36:1 was passed at a flow of 3.6 liters per minute. The reaction after initiation was autothermio. The efiiuent gas contained 8.2% C2H2.

Essentially pure carbon monoxide and hydrogen were obtained as by-products of the process as the raw material of hydrocarbon character undergoing treatment was substantially decomposed. The efiiuent gas contains, in addition to acetylene, carbon monoxide and hydrogen approximately in the ratio 1:2 as to constitute a valuable gas for the synthesis of alcohols or for the production of hydrogen.

In these processes, the reaction occurs in a single state of heating and the gases are premixed i. e. mixed before entering the reaction zone.

The procedure is applicable at atmospheric and subatmospheric pressures, although at the latter condition, higher yields of acetylene are possible in shorter time intervals.

A feature not described nor disclosed by the prior art is the incomplete combustion of gaseous mixtures, using linear gas velocities essentially above the respective flame velocity of the gas mixture but maintaining a flame combustion by suitable means, for example as described heretofore. For example, by subjecting a mixture of methane and oxygen to incomplete combustion at a linear gas velocity equal to the flame velocity, I realized only about 0.7% acetylene in the effluent gases. Carrying out the process with the identical mixture with a gas velocity greater than the flame velocity I was able to obtain a concentration of about 6.2% acetylene in the efiiuent gases.

While I have in the foregoing described in some detail the preferred embodiment of my invention and some variants thereof, it will be understood that this is only for the purpose of making the invention more clear and that the invention is not to be regarded as limited to the details of operation described, nor is it dependent upon the soundness or accuracy of the theories which I have advanced as to the reasons for the advantageous results attained. On the other hand, the invention is to be regarded as limited only by the terms of the accompanying claims, in which it is my intention to claim all novelty inherent therein as broadly as is possible in view of the prior art.

I claim as my invention:

1. A method for producing acetylene, comprising: burning in an enclosed apparatus a mixture of gases containing a hydrocarbon and oxygen, the oxygen content being less than half the amount necessary for complete combustion, the linear gas velocity being maintained essentially above the respective flame velocity of the gas mixture in the combustion zone, while maintaining flame combustion.

2. A method for producing acetylene, comprising: burning in an enclosed apparatus a mixture of gases containing a hydrocarbon and oxygen, the oxygen content being less than half the amount necessary for complete combustion, the linear gas velocity being maintained essentially above'the respective flame velocity of the gas mixture in the combustion zone while maintaining flame combustion by confining the heat of combustion in the reaction zone.

3. A method for producing acetylene, comprising: burning in an enclosed apparatus a mixture of gases containing a hydrocarbon and oxygen, the oxygen content being less than half the amount necessary for complete combustion, the linear gas velocity being maintained essentially above the respective flame velocity of the gas mixture in the combustion zone while maintaining flame combustion by conducting it on a surface of refractory material.

4. A method for producing acetylene, comprising: burning in an enclosed apparatus a mixture of gases containing a hydrocarbon and oxygen, the oxygen content being less than half the amount necessary for complete combustion, the linear gas velocity being maintained essentially above the respective flame velocity of the gas mixture in the combustion zone while maintaining flame combustion by externally heating the wall of the reaction chamber.

5. A method for producing acetylene, comprising: burning in an enclosed apparatus a mixtureof gases containing a hydrocarbon and oxygen,

the oxygen content being less than half the amount necessary for complete combustion, the linear gas velocity being maintained essentially above the respective flame velocity of the gas mixture in the combustion zone while maintaining flame combustion by a pilot flame.

6. A method for producing acetylene, comprising: burning in an enclosed apparatus a mixture of gases containing a hydrocarbon and oxygen, the oxygen content being less than half the amount necessary for complete combustion, the linear gas velocity being maintained essentially above the respective flame velocity of the gas mixture in the combustion zone while maintaining flame combustion by a pilot flame whose flame velocity is not less than the gas velocity of the gas mixture being burned as the pilot flame.

7. Same as claim 6 wherein the gas mixtures fed to the pilot flames contain more oxygen than the main gas jet.

8. A method for producing acetylene, comprising: burning in an enclosed apparatus a mixture of gases containing a hydrocarbon and oxygen, the oxygen content being less than half the amount necessary for complete combustion, the linear gas velocity being maintained essentially above the respective flame velocity of the gas mixture in the combustion zone while maintaining flame combustion by pilot flames burning from separate nozzles fed with pure oxygen which burns as an inverted flame in the rest of the gas mixture.

9. A method for producing acetylene, comprising: burning in an enclosed apparatus a mixture of gases containing a hydrocarbon and oxygen, the oxygen content being less than half the amount necessary for complete combustion, the

linear gas velocity being maintained essentially above the respective flame velocity of the gas mixture in the combustion zone while maintaining a flame combustion by conducting it on a refractory surface, allowing the reaction zone to ing: eflecting the incomplete combustion of a gaseous mixture of hydrocarbon and oxygen, the

oxygen content being less than half the amount necessary for complete combustion, at a temperature above 850 C. in the form of surface combustion on refractory material, the linear gas velocity exceeding the flame velocity of the gas mixture in the combustion zone and confining the heat of combustion in the reaction zone while maintaining flame combustion.

13. A method for producing acetylene, comprising: pre-mixing a hydrocarbon and an oxygen-containing gas, the oxygen content being less than half the amount necessary for complete combustion, and subjecting them to incomplete combustion at a temperature exceeding, 1000 C. while confining the heat of combustion in the reaction zone, the linear gas velocity exceeding the flame velocity of the gas mixture in the combustion zone while maintaining flame combustion.

14. A method for producing acetylene, comprising: pre-mixing a hydrocarbon and an oxygen-containing gas, the oxygen content being less than half the amount necessary for complete combustion, and subjecting them in the presence the flame burning in an outside atmosphere crecountercurrent heat exchange to the reaction 16. A method for producing acetylene which comprises subjecting to incomplete combustion, in an enclosed apparatus, hydrocarbon with less than one-half the amount of oxygen necessary for complete combustion, the linear gas velocity being maintained essentially above the respective flame velocity ofthe gas mixture in the combustion zone while maintaining flame combustion,

ated by the discharge gases of the flame.

17. A method for producing acetylene which comprises subjecting to incomplete combustion, in an enclosed apparatus, natural gas with less than one-half the amount of oxygen necessary 5 for complete combustion at above the ignition temperature of the gaseous mixture, the linear gas velocity being maintained essentially above the respective flame velocity of the gaseous mixture in the combustion zone while maintaining flame combustion.

JAMES BURGIN. 

